The present invention relates to a method of forming an optical waveguide, particularly to a method of forming a waveguide by ion implantation.
Several methods have been proposed for forming an optical waveguide in a glass substrate by ion implantation. According to the method reported by I. K. Naik (Appl. Phys. Lett., vol, 43, No. 6, pp. 519-520), nitron ions are implanted into the surface of a substrate made of fused quartz, optical glass, SiO.sub.2 -coated silicon, etc. and the substrate is then subjected to a heat treatment at 460.degree. C. for 30 min. Naik reported that an optical waveguide suffering a loss of as low as 0.1 dB/cm could be obtained by this method.
However, the above-described method of forming an optical waveguide by ion implantation has had the serious problem that when the substrate implanted with nitrogen ions was heat-treated at temperatures higher than 500.degree. C., the concentration of nitrogen in the substrate decreased so drastically that the formed optical waveguide disappeared.